1. Field of the Invention
This invention relates to apparatus for the production of heat softenable materials and more particularly relates to apparatus for the production of felted mat or blankets of mineral fibers.
2. Discussion of the Prior Art
Heretofore blankets of mineral fibers have been produced by various techniques involving the formation and attenuation of fibers from a molten mass and the collection of those fibers, usually on a continuously moving foraminous belt in the form of an endless screen or chain surface. The attenuation of fibers has been accomplished by a rotary process wherein a molten stream of the material to be fiberized impinges upon a rotating surface and flows therefrom as fine fibers under the influence of centrifugal force and gas flow to a fiber collection conveyor. Rotary process fibers are relatively short and therefore less desirable for some applications than those fibers produced by gas attenuation. In the gas attenuation process filaments are exuded and/or drawn from a molten supply of materials and subjected to a high velocity gas blast to be attenuated. One technique involves drawing the material to solid filaments, primary filaments, and directing a gas blast of a temperature to remelt the filaments generally normal to the primary filament path of travel.
In both the rotary and gas blast processes of producing fibers the equipment required has been of a nature which severely limited the range of product which could efficiently be produced on a given machine. In general the past developments have been directed to means for producing fiber in quantities which could be incorporated in practical products at commercially acceptable rates and cost. R. H. Barnard U.S. Pat. No. 2,565,941 which issued Aug. 28, 1951 for "Method and Apparatus for Producing Laminated Materials" discloses a plurality of drawing chambers for producing glass fibers attenuated by the gas blast method. These fibers are collected in collecting chambers from which they issued and are laid down in succession on a conveyor. The output of the Barnard arrangement was limited since the quantity of fiber issued from each forming chamber under the impetus of gravity and the attenuating gas blast was quite limited.
Fiber output for the gas blast attenuated processes has been increased by utilizing a large number of fiber attenuators arranged to deposit the attenuated fibers on a collection conveyor on the opposite side of which negative pressure is maintained to draw the fibers to the collection conveyor. Forming tubes have been utilized to direct the fibers from their spaced attenuators to the more confined collection region as shown in Labino U.S. Pat. No. 3,076,236 for "Apparatus for Making Mats of Blown Mineral Fibers" which issued Feb. 5, 1963. Such process are limited by the effective fiber directing suction which can be maintained on the fiber receiving face of the collection conveyor as the fiber blanket builds since the blanket becomes an impediment to the gas flow which entrains the fibers.
One means of incresing the negative pressure where the entraining gas flow is restricted by previously deposited fibers is to provide separate suction boxes behind the fiber collection conveyor as in W. F. Rea U.S. Pat. No. 2,961,698 for "Process and Apparatus for Producing Fibrous Mats." In this arrangement a first fiber former has a collection chamber across the bottom of which is passed a fiber collection conveyor backed by a suction box. The fiber collection conveyor then advances the blanket to a position where a septum or reinforcement material is laid upon the blanket and then to a second fiber former having a separate collection chamber and suction box. While the second suction box can be controlled as to its negative pressure, the constraints of reduced pressure due to the impediment to gas flow of the previously deposited blanket and septum remain as limits on the fiber depositing capacity of the system.
Another form of apparatus for formation of composite fiber blanket is suggested in Slayter U.S. Pat. No. 2,457,784 wherein it is proposed that a plurality of mats be fed to a station where they are juxtaposed and manipulated to interfelt their fibers.